High gasoline prices and bad weather may even tempt more shoppers to do more holiday shopping online this year, he said.

In a report released Monday, Forrester Research Inc. analyst Carrie Johnson said online sales will rise by 25 percent to $18 billion between Thanksgiving and Christmas. However, the Web is not insulated from off-line concerns like rising gas prices, she said in the report. That means if off-line retailers suffer, so will their online counterparts.

"If consumers are worried about paying $50 for gas, they're not going to jump online to spend their hearts out," Johnson said in the report.

However, online retailers are expected to benefit from new shoppers this year. "Three and a half million new households began shopping online in 2004, and we're expecting another 2.5 million to join them in 2005," Johnson said.

In addition, free shipping offers could drive up the average size of online orders this season, she said.